1. Field of the Invention
The present invention relates generally to a telephone headset utilizing a microphone boom. More specifically, a telephone headset utilizing a foldable microphone boom that is operable in both noise canceling and omnidirectional modes is disclosed.
2. Description of Related Art
With increasing usage of mobile communications devices such as cellular telephones as well as increasing reliance upon telephones as a preferred mode of communication, both in business and personal settings, telephone headsets are gaining popularity in a variety of applications. Some commercially available headsets have long booms that place the acoustic sensing point near the user's mouth while others have short booms or no booms at all. The term “acoustic sensing point” is used herein to refer to the location or point in space where a headset collects sound waves.
In some headsets, the microphone is located directly at the acoustic sensing point at the distal end of a boom. One example of such a microphone is a noise canceling microphone. A noise canceling microphone is generally direction sensitive, i.e., it is more sensitive to incoming acoustic signal in certain directions and less sensitive in other directions. When used in a noisy environment, the noise canceling microphone can increase the user's voice signal-to-ambient noise ratio. The noise canceling microphone is typically placed at the end of a long boom such that when the microphone is positioned to aim at the user's mouth, the user's voice approaches the microphone in or near the direction of maximum sensitivity for the microphone. The ambient noise, on the other hand, is usually diffused and approaches the microphone from many different directions. Thus, only a small portion of the ambient noise approaches the microphone in the directions of high sensitivity. Even if the noise source is non-diffused such as where the noise originates from one or a few specific directions, there is a high probability that a large portion of the noise approaches from directions in which the microphone is relatively insensitive.
In addition, noise canceling microphones have higher near field to far field sensitivity ratio, known as “proximity effect,” than omni-directional microphones. The proximity effect results from the acoustic pressure gradient between the arrival of the sound waves to the front and to the rear of the noise canceling microphone's diaphragm. The proximity effect causes noise canceling microphones to have higher user's voice signal-to-ambient noise ratios than omni-directional microphones.
The advantages of a noise canceling microphone can be realized generally only if the acoustic sensing point is close to the user's mouth and appropriately positioned. In order to satisfy these conditions, a sufficiently long boom is generally required that provides the user with enough flexibility to position the microphone close to and aim the microphone towards the user's mouth. The superior performance of a noise canceling microphone depends on the proximity effect and on the assumption that the noise is diffuse or that it approaches from an angle outside the maximum sensitivity range of angles associated with the microphone, which is not always valid. Moreover, noise canceling microphone is known to be more susceptible to wind noise than omni-directional microphone.
A long boom, which places the acoustic sensing point near the user's mouth, as required for effective noise canceling, is not always desirable for users. A headset with a short boom or no boom at all is typically more appealing because of its unobtrusive and stylish appearance and easy stowability. This is particularly true for users of portable communication applications such as mobile phones.
When a short boom or boomless headset is used, the distance between the user's mouth and the acoustic sensing point of the headset is relatively large and an omni-directional microphone is typically used. An omni-directional microphone has a sound port on one side of the microphone diaphragm, in contrast to both sides of the microphone diaphragm in the case of a noise canceling microphone. When used in noisy environments, a headset with an omnidirectional microphone generally provides a lower than desirable user's voice signal-to-ambient noise ratio. However, because of the unobtrusive and stylish appearance and easy stowability of compact short boom or boomless headset, users continue to demand this type of headsets in many applications.
However, when a headset is used in conjunction with a mobile communications device such as cellular telephone, the headset is generally required to provide consistently high transmit signal quality especially in noisy environments. For example, it would be advantageous to reduce the obscuring effect of ambient noise in the transmit signals when the headset is used outdoors.
A headset with a foldable boom is available as a compromise between the desire for compactness and style and the need for satisfactory transmit signal quality. Typically, such a headset with a foldable boom have an inoperable compact mode in which the boom is folded on top of the body for storage and an extended-boom mode in which the headset is operable with adequate transmit signal quality. When the boom is folded on top of the body to place the headset in the compact mode for storage, the acoustic sensing point typically ends up behind the user's ear where it is generally too far from the user's mouth to assure a sufficient transmit signal level and signal-to-noise ratio at normal speech levels. Because the headset is inoperable when the headset is in the compact mode, the user is still required to extend the boom in this conventional headset with foldable boom in order to utilize the headset.
Thus, what is needed is a headset that provides both the unobtrusive and stylish appearance and easy stowability of a compact short boom utilizing an omnidirectional microphone for application in a less noisy environment and satisfactory transmit signal quality of a longer boom utilizing a noise canceling microphone for application in a noisy environments. Preferably, the headset has multiple modes of operation, including a noise canceling mode and a compact mode for when noise is not an issue.